The present disclosure relates to a gas turbine structure. Moreover, the present disclosure relates to a gas turbine engine. Furthermore, the present disclosure relates to an aeroplane.
A gas turbine engine may be used as a jet engine. The term jet engine includes various types of engines, which admit air at relatively low velocity, heat it by combustion and shoot it out at a much higher velocity.
Accommodated within the term jet engine are, for example, turbojet engines and turbo-fan engines. The invention will below be described for a turbo-fan engine, but may of course also be used for other engine types.
A gas turbine structure, which may sometimes be denoted a case or frame, is used for supporting and carrying bearings, which in turn, rotatably support rotors. Conventional turbo hut engines have a fan frame, a mid-frame and an aft turbine frame. These frames constitute a gas turbine structure including a first housing, a second housing and a strut or a vane having a first end of the strut or vane being attached to the first housing and a second end being attached to the second housing.
Depending on the position of the gas turbine structure in the gas turbine, the gas turbine structure, and in particular the strut and/or vane thereof, may be imparted large loads, such as thermal loads from the gas path temperature.
In order to reduce the thermal load on the vane, U.S. Pat. No. 4,993,918 proposes that the vane is furnished with a fairing extending from a first ring to a second ring. However the provision of a '918 fairing makes inspection of the enclosed vane difficult. Additionally, it may be difficult to replace a '918 fairing, again due to the tight tolerances required for the fairing.
It is desirable to provide a gas turbine structure which overcomes or ameliorates at least one of the disadvantages of the prior art, or to provide a useful alternative.
As such, the present disclosure relates to a gas turbine structure comprising a first housing and a second housing, one of the first and second housings being located around the other of the first and second housings such that a core flow passage is obtained between the first and second housings. The gas turbine structure further comprises an elongate structural member extending in a structural member direction from the first housing to the second housing.
According to the present disclosure, the gas turbine structure may preferably be used in a position in a gas turbine such that a hot core flow is guided between the first and second housings, i.e. that a hot core flow passage is obtained between the first and second housings. As such, the gas turbine structure of the present disclosure may preferably be intended to be positioned downstream of a combustor of a gas turbine.
As used herein, the expression “housing” relates to member which has at least a circumferential extension. However, the circumferential extension does not necessarily have to be circular but may in some implementations of the housing instead be oval, rectangular or any other type of shape.
The structural member between the first and second housings is often referred to as a strut or a vane. As used herein, the expression “strut” relates to a structural member which has a symmetrical cross section with respect to the intended flow direction of the core flow passage whereas the expression “vane” relates to a structural member which has an asymmetrical cross section with respect to the intended flow direction.
The gas turbine structure further comprises a fairing circumferentially enclosing at least a portion of the structural member; the fairing extends in a fairing direction which is substantially parallel to the structural member direction.
The fairing comprises a fairing attachment portion, attached to the first housing such that a displacement at least in said fairing direction of said fairing attachment portion in relation to said first housing is prevented. The fairing further comprises a fairing end portion located at the other end of the fairing in the fairing extension direction as compared to the fairing attachment portion. The fairing end portion is allowed to be displaced, in at least the fairing direction, in relation to the second housing.
Preferably, the fairing end portion is allowed to be displaced, in at least the fairing direction, in relation to the second housing by virtue of the fact that the gas turbine structure comprises a gap, measured in the fairing direction, between the fairing end portion and at least a portion of the second housing.
With a gas turbine structure according to the above, a portion of the faring is locked from displacement, at least in the fairing extension, in relation to the first housing but not in relation to the second housing. The above implies that the fairing may be allowed to expand, e.g. when subjected to thermal loads, which results in that contraction forces in the fairing may be low and in some embodiments of the present disclosure the contraction forces in the fairing may even be removed.
Moreover, since the fairing is not attached to the second housing, there is often not a need for manufacturing the fairing with close tolerances, at least not with close tolerances of the fairing in the fairing direction. Thus, the gas turbine structure according to the above implies that the manufacturing cost and/or manufacturing time may be reduced as compared to prior art gas turbines having struts which are furnished with fairings attached to the first housing as well as the second housing.
Furthermore, the fact that the fairing is not attached to the second housing may facilitate the replacement of a fairing.
Additionally, since the structural member is located in the core flow passage, the structural member may be subjected to thermal loads when the gas turbine, of which the above gas turbine structure forms a part, is operated. However, since the fairing may cover at least a portion of the structural member, the thermal loads imparted on that portion may be reduced. This in turn implies that the portion of the structural member may be made of a material with lower thermal characteristics as compared to a gas turbine structure without fairings.
The design and the material of the portion of the structural member which is covered by the fairing could instead be chosen with a focus on an appropriate structural capacity. As such, by virtue of the use of a fairing, the covered portion of the structural member may be designed with fewer constraints on the shape of the structural member and the first or second housing due to the separated functionality between the structural member and the fairing. On the other hand, the fairing may be designed with a focus on an appropriate thermal capacity and/or on appropriate aerodynamic properties.
Purely by way of example, each one of the fairing and the portion of the structural member which is covered by the fairing may comprise a leading edge and a trailing edge. Each one of the radius of the leading edge and the radius of the trailing edge of the fairing may be relatively small such that appropriate aerodynamic properties of the fairing are obtained whereas the radii of the leading and trailing edges of the covered portion of the structural member may be relatively large, i.e. at least larger than the radii of the fairing, in order to obtain appropriate structural properties of that portion of the structural member. Moreover, the radii of the structural member may increase towards the first housing.
Purely by way of example, the radius of the leading edge of a covered portion of the structural member may be 5 times larger, preferably 10 times larger, than the radius of the leading edge of the fairing covering that portion of the structural member. In a similar vein, and again purely be way of example, the radius of the trailing edge of a covered portion of the structural member may be 5 times larger, preferably 10 times larger, than the radius of the trailing edge of the fairing covering that portion of the structural member.
According to the present disclosure, the structural member may comprise a first stand-up and an intermediate member. The first stand-up may be attached to the first housing and the intermediate member may be attached to the first stand-up by means of a first stand-up joint. At least a portion of the fairing may extend past the first stand-up joint in the structural member direction.
As has previously been discussed, the stand-up, which thus constitutes at least a portion of the structural member which is at least partially covered by the fairing, may be designed with a focus on an appropriate structural capacity. The intermediate member, or at least the portion of the intermediate member extending past the fairing in the structural member direction, may be made of a material with better thermal characteristics, e.g. a higher thermal resistance, than the first stand-up.
According to the present disclosure, the structural member may have a structural member length in the structural member direction from the first housing to the second housing and the fairing may have a fairing length from the first housing in the fairing direction. The fairing length may be smaller than the structural member length. However, the fairing length may preferably be at least 10 mm.
According to the present disclosure, the fairing length may be less than 90%, preferably less than 50%, more preferred less than 30%, of the structural member length.
A fairing having a fairing length in any of the above ranges implies that a replacement of the fairing is straightforward. Moreover, a fairing length with any of the above ranges may render an inspection, such as a visual inspection, of the fairing and/or the structural member possible.
According to the present disclosure, the structural member may comprise a leading structural member portion and a trailing structural member portion, the trailing structural member portion may be arranged to be located downstream of the leading structural member portion when the gas turbine engine is operated to produce a core fluid flow through the gas turbine structure. The fairing may comprise a first fairing portion and a second fairing portion wherein the first fairing portion may cover the leading structural member portion and the second fairing portion may cover the trailing structural member portion. The first fairing portion and the second fairing portion may contact one another in a contacting area comprising a first axial split line and a second axial split line.
The above implementation of the fairing may facilitate a process step of mounting and/or replacing a fairing.
According to the present disclosure, the fairing may comprise a leading edge and a trailing edge. Moreover, the fairing may extend from the leading edge to the trailing edge along a mean camber line.
The mean camber line is defined as the locus of points halfway between the leading edge and the trailing edge as measured perpendicular to the mean camber line itself.
The fairing may further have a fairing thickness measured in a direction perpendicular to the mean camber line. The fairing may further have a maximum thickness between the leading edge and the trailing edge and the fairing may also have a suction side and a pressure side. The first axial split line may be located on the suctions side between the maximum thickness and the trailing edge when measured along the mean camber line.
With the above position of the first axial split line, the first axial split line may have a low influence on the flow around the fairing.
According to the present disclosure, the second axial split line may be located on the pressure side and the second axial split line may be located closer to the leading edge, when measured along the mean camber line, than the first split line.
The above position of the second axial split line implies that the first fairing portion and the second fairing portion may be at least similar in size. This may be advantageous from e.g. a fairing manufacturing, fairing handling and/or fairing mounting point of view.
According to the present disclosure, the forward portion may overlap the rearward portion in the contacting area. The above overlap may result in that the flow around the fairing is not adversely impaired, at least not to any greater extent.
According to the present disclosure, each one of the first fairing portion and the second fairing portion may comprise a sheet metal portion.
According to the present disclosure, the structural member may comprise a structural member outer surface and the fairing may comprise an inner fairing surface. The gas turbine structure may further comprise a fairing gap being the distance in a direction normal to the structural member outer surface from the structural member outer surface to the fairing inner surface. The gas turbine structure may comprise a fairing closure and the fairing closure may be configured such that the fairing gap at the fairing closure is smaller than the average fairing gap at the remaining portion of the fairing.
The fairing closure may reduce the amount of hot gas entering a volume enclosed between the fairing and the structural member. This in turn may result in a reduced thermal loading on at least a portion of the structural member.
According to the present disclosure, the smallest distance between the fairing closure and the structural member may be less than 50%, preferably less that 30%, of the smallest distance between the remaining portion of the fairing and the structural member.
According to the present disclosure, the fairing closure may comprise a flanged portion of said fairing.
According to the present disclosure, the fairing may be attached to the first housing by means of a releasable joint, preferably a bolt and/or a rivet joint.
According to the present disclosure, the gas turbine structure may comprise an additional fairing circumferentially enclosing at least a portion of the circumference of the structural member. The additional fairing may extend in an additional fairing direction substantially parallel to the structural member direction. Moreover, the additional fairing may comprise an additional fairing attachment portion attached to the second housing such that a displacement of the additional fairing attachment portion in relation to the second housing is prevented at least in the additional fairing direction. Furthermore, the additional fairing may comprise an additional fairing end portion located at the other end of the additional fairing in the additional fairing extension direction as compared to the additional fairing attachment portion. The additional fairing end portion may be allowed to be displaced, in at least the additional fairing direction, in relation to the first housing.
According to the present disclosure, the gas turbine structure may comprise a plurality of structural members.
According to the present disclosure, a plurality of the structural members may comprise a fairing.
According to the present disclosure, the gas turbine structure may be a rear gas turbine structure.
A second aspect of the present disclosure relates to a gas turbine engine comprising a gas turbine structure according to the first aspect of the present disclosure.
A third aspect of the present disclosure relates to an aeroplane comprising a gas turbine engine according to the second aspect of the present disclosure.
Further advantages and advantageous features of the disclosure are disclosed in the following description and in the dependent claims.